All You Wanted to Know About USB Power (But Didn’t Know How to Find Out)

Here’s a little gadget that few of us need, but at only $10, some of us might decide to get, anyway.

I found it useful when testing a new six-port USB charger that claims to charge up six devices simultaneously, and all at fast charges/high current.  Did it really provide up to 10A of charging power (the answer seems to be yes, and with no voltage drop either)?

Actually, it is also helpful/interesting to use it with all the USB chargers I’ve amassed so as to see which ones will best/fastest charge which devices, and which ones can be nobly retired to the trash bin.  Sometimes a USB charger has a very low maximum current output, and other times, it is not able to ‘talk’ properly to modern devices and negotiate a higher than default 0.5 Amp charge rate.

Over the years there have been many changes to how USB devices and chargers manage their rate of charging, and it is hard to know which chargers work best with which devices, and only recently are some semi-universal standards appearing in an attempt to quality control all of this.

One other point of curiosity is how devices handle being connected to a charger when fully charged.  Do they continue to consume unnecessary power and possibly damage their batteries or do they switch off and not take more charge?

These issues apply not only to chargers, but also to USB ports on computers and to external USB hubs.

For example, a less critical factor but sometimes still interesting to know is the voltage output from the USB charger, both off-load and on-load.  Some computers (particularly laptops) – and also USB hubs – might experience significant voltage drops when connected to heavy loads, and that could cause problems, particularly if other voltage-sensitive devices were also connected.

These questions are interesting to some of us, and are normally difficult to answer.  It has been possible to get little ‘break out boards‘ that allow you to connect some types of test equipment – multimeters and oscilloscopes – in series or parallel to a USB circuit, and for some of us, that’s a very flexible way of ‘opening up’ the USB circuit for any type of experimentation and monitoring we might wish.

But if you’re not quite such an avid enthusiast and without an array of additional test equipment, there’s now an easy and inexpensive solution that gives a wonderfully clear and simple answer to the types of questions listed above.  The unit pictured above.

A number of companies seem to be branding and selling the same unit, and it can be found on Amazon for around the $10 price point (if shipped from China) or around the $15 point (if Amazon ships it from the US and with ‘free’ fast delivery).  Yes, the more pedantic of us might question the use of the word ‘free’ but if you’re as impatient as I often am, you’ll doubtless end up paying the $15 rather than saving $5 and waiting potentially a month for the unit to arrive from China.

Amazingly, a plain break out board with no displays and not even a box costs about $12, so one of these complete integrated dual display units is a great bargain.

Using the Unit

The unit is very simple and easy to use.  Plug it into a USB port and it immediately starts monitoring the voltage.  Plug something into the unit and it will then start monitoring the power that flows through the unit as well.

It has two ports to plug things into, and claims to be able to monitor and pass through up to 3A of power.  One port works better with Android devices and the other with Apple devices.  Which is which?  The bad news is the unit comes with no instructions at all; the good news is you can simply plug devices into both sides to see which side gives the greater current draw.

The unit claims to be accurate to within 1% and has three digit displays for both volts and amps.  I don’t have any test equipment that is as accurate as that, so can’t confirm this slightly improbably claim, and so will simply observe that if this is true, the third of the three digits isn’t very accurate while the first two are probably reasonably correct.  Many electronic devices these days fall into the trap of displaying more digits of data than they are accurate to show.

It has been interesting to compare various chargers – for example, if I connect to a port on my laptop, the voltage drops way down to 4.7V when trying to charge an iPad, and one of the ports actually gives the iPad an impressive 1.5A of power.  On the other hand, an official Apple charger goes over 2A and stays at closer to 5V, but if I connect an Android device to the iPad charger, it refuses to give more than 0.44 A of power.

Knowing which chargers give the fastest charge can actually be helpful, particularly when traveling, and you have a short amount of time and a lot of devices to quickly top up.

I’ve also used it in my car, to note that one car cigarette lighter charger struggles to give a mere 0.73A of power, and its voltage drops to 4.4V while doings so, whereas the other goes up to 2A, confirming something I’ve sensed but not known for sure – that phones charge faster on one charger in one car then on the other charger in the other car.

With the modern iPhones taking potentially 2A of power, a high power car charger really makes a difference, and I’ve noticed that when using the GPS in my iPhone 6+, the 0.73A charger barely maintains the level of charge in the phone.  That’s definitely going to be upgraded to one of the lovely four port fast chargers we have in the other car – at only $17, that’s a no-brainer upgrade.

The device has been – and still is – fun to use.  If you’re a bit of a techie type yourself and like knowing more about these sorts of issues, the chances are you’ll find the $10 – $15 to be well spent, too.  But if you’re still wondering what the difference between V, A and W is, and don’t really care other than that your devices charge when plugged in, there’s no need to complicate your life any further!

As you’ll see on the linked Amazon page, there are a wide range of these devices, many of which look the same, and some of which are clearly different.  All the similar looking units are thought to be identical, with the only difference between the company providing it and the price it is charged for.  Buy either the cheapest (with slow delivery) for around $10, or pay a few dollars more for faster delivery.